The present invention is related to a high pressure pump for pressurizing and supplying fluid, and more particularly, to a high pressure pump that is optimal for pressurizing and supplying fuel to a fuel injection valve of a vehicle engine.
Japanese Laid-Open Publication No. 8-68370 discloses a high pressure fuel pump used for a vehicle engine. The high pressure fuel pump has a cylinder, a plunger that is inserted into the cylinder, and a lifter that moves the plunger axially direction with respect to the cylinder. As the plunger reciprocates, the plunger pressurizes fuel in a pressurizing chamber, which is defined in the cylinder, and discharges the fuel from the pressurizing chamber.
The lifter contacts one end of the plunger that is projected from the cylinder. The lifter is slidably supported by a pump housing. A generally cylindrical seal member is attached to the cylinder so as to surround the portion of the plunger that is projected from the cylinder. The seal member has an annular lip portion defined at its distal end. The annular lip portion contacts an outer peripheral surface of the plunger. The seal member prevents fuel, which leaks from the pressurizing chamber through a clearance between the cylinder and the plunger from mixing with lubricating oil that lubricates the lifter.
FIGS. 4(a) and 4(b) are cross sectional views of a plunger 43 and a seal member 41. Although not shown, a cylinder is positioned upward of FIGS. 4(a) and 4(b), and a lifter is positioned downward of FIGS. 4(a) and 4(b). The seal member 41 disconnects a cylinder side space (the space surrounded by the seal member 41) from a lifter side space (the space outside the seal member 41). The lip portion 42 of the seal member 41 has an upper lip 42a and a lower lip 42b that are spaced from each other in the axial direction of the plunger 43. The upper lip 42a prevents fuel L1 collected on the peripheral surface of the plunger 43 from entering the lifter side space. The lower lip 42b prevents that lubricating oil L2 invades into the cylinder side space. Therefore, fuel and lubricating oil are prevented from mixing.
When the plunger 43 moves in a direction projecting out of the cylinder, that is, when the plunger 43 moves downward in FIG. 4(a), the fuel L1 collected on the peripheral surface of the plunger 43 is removed by the upper lip 42a. The removed fuel L1 is stored in the cylinder side space and prevented from entering the lifter side space. On the other hand, when the plunger 43 moves in a direction entering the cylinder, that is, when the plunger 43 moves upward in FIG. 4(a), the lubricating oil L2 collected on the peripheral surface of the plunger 43 is removed by the lower lip 42b and prevented from entering the cylinder side space.
However, it is difficult to completely remove the fuel L1 and the lubricating oil L2 collected on the plunger 43 by the lip portion 42. Therefore, in the high pressure fuel pump of the above publication, the mixing of the fuel and the lubricating oil is not sufficiently prevented. When the fuel leaks into the lifter side space and mixes with the lubricating oil, the lubricating oil is diluted and the lifter cannot be lubricated sufficiently.
When the plunger 43 moves from the highest position shown in FIG. 4(a) to the lowest position shown in FIG. 4(b), the fuel L1xe2x80x2 that is not removed by the upper lip 42a temporarily enters the space between the upper lip 42a and the lower lip 42b and then passes by the lower lip 42b to leak into the lifter side space.
When the plunger 43 moves from the lowest position shown in FIG. 4(b) to the highest position shown in FIG. 4(a), the lubricating oil that is not removed by the lower lip 42b temporarily enters the space between the upper lip 42a and the lower lip 42b and passes by the upper lip 42a to leak into the cylinder side space.
As the stroke of the plunger 43 lengthens to increase the discharged amount of the fuel, the leakage amount of the fuel and the lubricating oil increases.
It is an object of the present invention to provide a high pressure pump for that guarantees prevention of fluid leakage from one of two spaces, which are disconnected by a seal member, into the other one of the two spaces.
To achieve the above object, a high pressure pump includes a cylinder having a pressurizing chamber. A plunger is inserted in the cylinder. The plunger is axially reciprocated with a predetermined stroke to pressurize fluid in the pressurizing chamber. The plunger has a projected portion projected from the cylinder. A drive member drives the projected portion to reciprocate the plunger. A seal member encompasses the projected portion. The seal member has an annular lip portion that contacts a peripheral surface of the projected portion. The annular lip portion has a pair of lips separated from each other in an axial direction of the plunger. An axial distance between the lips is greater than the stroke of the plunger.